Around 30 Gt of CO2 are released every year as an effect of human activities, mostly because of fossil fuel combustion. The huge amount of CO2 accumulating in the atmosphere since the beginning of the industrial era represents an inexpensive, ubiquitous and oil-free source of carbon for the chemical industry, as well as an environmental threat, given the high global warming potential of CO2. Therefore, the conversion of waste CO2 into value-added chemicals would be extremely advantageous. Nevertheless, as power generation and CO2 emission are unavoidably connected to fossil fuel combustion, only a process able to convert CO2 efficiently under mild conditions of temperature and pressure (i.e. little to no energy input required) could act as actual CO2 recycling with a positive C-balance. The process should preferentially be carried out directly from a stream of industrial flue gas to avoid the energetic penalty associated with CO2 purification.
In this context, the exothermic reaction between epoxides and CO2 to yield cyclic carbonates represents an active field of research. Cyclic carbonates such as ethylene or propylene carbonate represent key intermediates towards the synthesis of dimethyl carbonate and glycols (e.g., the Asahi-Kasei process, route to polycarbonates). Moreover, ethylene and propylene carbonate are useful highly polar solvents for a wide range of applications including as solvents for electrolytes in batteries and for the painting industry.
Cyclic carbonates are generally produced by the reaction of epoxides and CO2 in the presence of metal halides and tetraalkylammonium salts. This process typically takes place at temperatures higher than 120° C. and at pressure above 40 bar and therefore is a net CO2 producer. Alternatively, cyclic carbonates can be prepared from phosgene and glycols. This process presents low yields, produces corrosive HCl gas and uses a very toxic reagent such as phosgene which is considered a weapon of mass destruction (WMD).
There is currently a strong effort by most industrialized countries to reduce CO2 emissions; International treaties such as the Kyoto Protocol have been signed by most UN member countries and mechanisms have been set in place to reward countries and firms able to abate emissions through the creation of quota systems and tradable emission credits. However no viable catalytic system existed so far for the conversion of CO2 and alkylene oxides at ambient temperature and at sub-atmospheric CO2 pressure under batch conditions or directly from a stream of diluted CO2 gas.
Therefore, there is a need to overcome the deficiencies of current technology.